The present invention relates generally to satellite packet communications systems, and more specifically to a spread packet communication system.
The slotted and unslotted ALOHA packet communication systems are well known. In these systems, very small aperture terminal (VSAT) stations randomly transmit their data packets in burst form via a satellite transponder to a central station. A modified version of the ALOHA system is the spread ALOHA network which was proposed in 1986 by Norman Abramson and is described in "Spread ALOHA for VSAT Networks", Norman Abramson, Technical Report B86-4b, University of Hawaii, June, 1986 (rev. January/1987). According to this technique, packet data from each VSAT station are distributed or "spread" on the time domain using a coded sequence of pseudorandom numbers in order to reduce the probability of burst collisions and to reduce per-bit transmission power. Two spread modes are known. One is the bit spread ALOHA in which each data bit is spread into a plurality of pseudorandom code bits, and the other is the chip spread ALOHA in which each pseudorandom code bit (or chip) is spread with the data bits of a packet. No implementations of the proposed spread ALOHA system have yet been made due to anticipated hardware complexities of central station's demodulator system which must be synchronized with high-speed chip-rate clock pulses to detect correlations between received data bits and a pseudorandom number (PN) sequence.